Back pain is a common problem and is difficult to treat. Because of the complex anatomy and poor correlation of pathology and symptoms, diagnosis of the etiology of the pain may be difficult. Typical diagnostic procedures seek to determine whether a patient experiences back pain, leg pain, or a combination thereof. Back pain describes pain localized to the back, and often includes pain in the buttocks and upper thigh areas. This type of pain is understood to be caused by changes in one or more intervertebral discs and is termed discogenic back pain. The recognition that discs are potential pain sources has been a relatively recent discovery and is supported by anatomical studies that demonstrate nerve fibers within the disc, often increased by degenerative processes, and by direct stimulation of discs during discectomy procedures while the patient is under aware-state analgesia. Other causes of back pain have also been described including zygopophyseal (facet) joints, and other unknown causes.
In contrast, leg pain is often due to impingement of nerve roots as they exit the spinal canal. This causes pain to radiate into the areas the nerves innervate and creates a dermatomal pattern of pain related to the normal pattern of the nerve supply. This radicular pain is often due to herniation of intervertebral discs such that they bulge into the foramenal space, entrapping and pressing on the nerve. It is also believed to result from nucleus pulposus material extruding from the disc, resulting in noxious stimuli from degradation products such as phospholipase A2, and cytokines such as interleukins and TNFa.
Because the treatments for back pain and leg pain are often different, it is important to establish a proper diagnosis. Indeed, there is a strong correlation between patient selection and outcomes for spinal procedures, such that meticulous attention to diagnosis is essential. This is especially true as patients often exhibit a pattern of symptoms. Even sophisticated imaging capabilities do not always provide a clear diagnostic picture. Other diagnostic tools, such as physical examination and determination of patient history, are important.
A staple of physical examination is palpation of the painful region, to pinpoint where the pain is emanating from. This is difficult in the case of the intervertebral disc as it is anatomically located deep within the body and surrounded by bony structures. A procedure known as discography, discogram, disc stimulation, or more precisely as provocative discography, has been developed to overcome this limitation. Discography involves placing a needle into the intervertebral disc using fluoroscopic guidance and then injecting a fluid to create pressure to stimulate the disc, analogously to palpation. The injected fluid is typically a saline solution including radiopaque dye to allow for assessment of the disc morphology. A manually operated syringe is generally used to inject the fluid. The patient is maintained in an aware state such that they can provide feedback as to the pain induced by the injection, i.e. pressurization of the disc. Injection is performed one disc level at a time with the injectionist, e.g., a physician, switching connections prior to the start of the test at a specific level.
Pressure manometry has been used to monitor the pressure applied to the disc. This provides a more objective means for the injectionist to control pressure as compared to determining the pressure based upon the feel of a manually operated syringe. Studies have demonstrated a better diagnostic correlation when patients respond to low to moderate pressures (<50 psi) as compared to higher pressures (>50 psi).
Another aspect of performing a reliable discography diagnosis is how the injectionist interacts with the patient to obtain feedback on the pain stimulation. A patient's response to pain can include two components: the magnitude of pain and the quality of pain. The magnitude is often described as ranging from 0 to 10, where 0 is no pain, and 10 is the worst pain imaginable. The quality of pain is described as being concordant, meaning the back pain they are complaining of, or not concordant, pain different from their complaint, such as a general feeling of pressure. The ability to distinguish between concordant and non-concordant pain improves the determination of whether the disc being stimulated is the root cause of a patient's back pain, or is evoking pain unrelated to their symptoms. A low pressure, concordant pain response at 1 or 2 spine levels, e.g., spinal discs, accompanied by no pain at a level above or below (control level) the painful discs is generally understood to provide the most definitive diagnosis for discogenic pain.
Patient responses from a discography procedure are recorded by the injectionist or assistant using one or more forms. Other parameters, such as the volume of fluid injected are added to the patient responses. A separate chart can be used to determine the peak pressure in the disc as well as any leakage.